This invention relates generally to electrical power generators and more particularly, to methods and system for detecting wedge tightness in an electrical power generator.
Armature windings, also known as stator bar windings, are routinely inspected in at least some known electrical power generators, to verify their operation. In some known generators, a stator yoke in the generator surrounds an armature core and partially encloses the armature windings. The stator windings are formed from a plurality of copper conductors that are wound in the armature to form loops. The armature windings may be arranged within a stator slot in such a manner that desired voltage and current characteristics may be maintained by the generator during operation.
At least one known generator includes a wedge system to induce a radial retaining force (RRF) to the stator from wedges to facilitate reducing movement of the stator bar windings within the stator slot. However, if the wedge system itself becomes loose, the amount of RRF is reduced such that the stator bar windings may move during operation. Over time, the relative motion of the stator bar windings cause damage to insulation surrounding the stator bar wedges, an/or a potential stator bar winding failure through electrical shorts to ground. Accordingly, within known generators, the wedge system is periodically inspected to determine if any stator bar winding movement within the stator slots exceeds predetermined tolerances.
Currently, several known methods of assessing the status of a wedge system are used. A first known method uses a hardness tester to assess the relative looseness of the stator wedges. A second known method requires tapping each individual wedge and listening to the response to determine whether the wedges are loose. A third known method includes exciting the vibrational modes of the stator wedges using multiple impacts, and receiving the energy transmitted from the multiple impacts using a band-pass filter to determine whether the wedges are loose. However, when the wedge system includes a top ripple spring, the above-described wedge system inspection methods may not accurately determine the tightness of the wedge system within the stator slot over the full range of operational wedge pressures when a top ripple spring system is used.